Kristian Olaf Bernhard Birkeland (13 December 1867 - 15 June 1917) was a Norwegian scientist who has been called "the first space scientist"[1] and "the father of plasma experiments in the laboratory and space"[2][3][4]. He is perhaps most well-known for his scientific work on the aurora using a terrella
(a magnetized globe), and as inventor of an electromagnetic cannon,
and, a method of electrically producing artificial fertilizer. He also
became a full professor of physics at the University of Oslo at the age
of 31.

Birkeland also had astrophysical research published on cathode rays,[5] the Zodiacal lights,[6] comets,[7] the Sun and sunspots,[8] the origin of planets and their satellites,[9] the Earth's magnetism.[10]
Some of Birkeland's other contributions to science included:[2] • Derived the general expression for the Poynting vector • Gave the first general solution to Maxwell's equations [11]
• Pioneered the field of charged-particle beams • Utilized the concept
of "longitudinal mass" • Constructed the first foil diodes • Pioneered
the field of visible-light photography of electrical discharges •
Advocated charged-particle propulsion engines for space travel • Created
Norsk Hydro's nitrogen-fertilizer industry (the Birkeland-Eyde method
for production of potassium nitrate) • Invented an electromagnetic rail
gun capable of firing a 10-kg projectile • Established Birkeland's
Firearms company • Anticipated cosmic rays (discovered in 1911) with his
calculations involving energies of several billion electron volts •
Held patents on the electromagnetic cannon,[12] electric blankets, solid margarine, and hearing aids.

In 1969 when field-align currents had been identified in the Earth's atmosphere, they were named in his honor: Birkeland currents.[13]....

He also co-founded Norsk Hydro and got his picture on the cover of the Rolling Stone Norway's 200 kr banknote:

The note will become invalid at the end of this year and the old boy will be replaced by a cod and a herring....

It was that Norsk Hydro bit that is important to this tale.
Norsk Hydro made nitrogen fertilizer using giant arcs to fix nitrogen in the air to nitric oxide which could be further manipulated to become nitric acid which can then be used to make explosives or fertilizer or other stuff. The process was very energy inefficient but hey, it was the early 20th century and we're talking Norway. They have a few waterfalls. Fast forward thirty years and despite the efforts of Birger and Andreas the Nazis have invaded and are intent on grabbing them some heavy water, of which Norsk Hydro has become the go-to source, as a byproduct of the now-modernized (no more Birkeland-Eyde process) fertilizer operation.

And it is here the story of February 28, 1943 really begins. From The Conversation via Scientific American:

Operation Gunnerside: The Norwegian Attack on Heavy Water That Deprived the Nazis of the Atomic Bomb

February 28 marks the 75th anniversary of one of the most dramatic and important military missions of World War II

The following essay is reprinted with permission from The Conversation, an online publication covering the latest research.
After handing them their suicide capsules, Norwegian Royal Army
Colonel Leif Tronstad informed his soldiers, “I cannot tell you why this
mission is so important, but if you succeed, it will live in Norway’s
memory for a hundred years.”

These commandos did know, however, that an earlier attempt at the same mission by British soldiers had been a complete failure.
Two gliders transporting the men had both crashed while en route to
their target. The survivors were quickly captured by German soldiers,
tortured and executed. If similarly captured, these Norwegians could
expect the same fate as their British counterparts, hence the suicide
pills.

Feb. 28 marks the 75th anniversary of Operation Gunnerside, and
though it hasn’t yet been 100 years, the memory of this successful
Norwegian mission remains strong both within Norway and beyond.
Memorialized in movies, books and TV mini-series, the winter sabotage of the Vemork chemical plant in Telemark County of Nazi-occupied Norway was
one of the most dramatic and important military missions of World War
II. It put the German nuclear scientists months behind and allowed the
United States to overtake the Germans in the quest to produce the first
atomic bomb.

So the U.S. atomic bomb arrived weeks too late for use against
Germany. Nevertheless, had the Germans developed their own bomb just a
few months earlier, the outcome of the war in Europe might have been
completely different. The months of setback caused by the Norwegians’
sabotage of the Vemork chemical plant may very well have prevented a
German victory.

Nazi bomb effort relied on heavy water
What Colonel Tronstad, himself a prewar chemistry professor,
was able to tell his men was that the Vemork chemical plant made “heavy
water,” an important ingredient for the Germans’ weapons research.
Beyond that, the Norwegian troops knew nothing of atomic bombs or how
the heavy water was used. Even today, when many people have at least a
rudimentary understanding of atomic bombs and know that the source of
their vast energy is the splitting of atoms, few have any idea what
heavy water is or its role in splitting those atoms. Still fewer know
why the German nuclear scientists needed it, while the Americans didn’t.

“Heavy water” is just that: water with a molecular weight of 20
rather than the normal 18 atomic mass units, or amu. It’s heavier than
normal because each of the two hydrogen atoms in heavy H2O weighs two
rather than one amu. (The one oxygen atom in H2O weighs 16 amu.) While
the nucleus of a normal hydrogen atom has a single subatomic particle
called a proton, the nuclei of the hydrogen atoms in heavy water have both a proton and a neutron—another
type of subatomic particle that weighs the same as a proton. Water
molecules with heavy hydrogen atoms are extremely rare in nature (less
than one in a billion natural water molecules are heavy), so the Germans
had to artificially produce all the heavy water that they needed.

In terms of their chemistries, heavy water and normal water behave
very similarly, and you wouldn’t detect any differences in your own
cooking, drinking or bathing if heavy water were to suddenly start
coming out of your tap. But you would notice that ice cubes made from heavy water sink rather than float when you put them in a glass of normal drinking water, because of their increased density.

Those differences are subtle, but there is something heavy water does
that normal water can’t. When fast neutrons released by the splitting
of atoms (that is, nuclear fission) pass through heavy water,
interactions with the heavy water molecules cause those neutrons to slow
down, or moderate.
This is important because slowly moving neutrons are more efficient at
splitting uranium atoms than fast moving neutrons. Since neutrons
traveling through heavy water split atoms more efficiently, less uranium
should be needed to achieve a critical mass;
that’s the minimum amount of uranium required to start a spontaneous
chain reaction of atoms splitting in rapid succession. It is this chain
reaction, within the critical mass, that releases the explosive energy
of the bomb. That’s why the Germans needed the heavy water; their
strategy for producing an atomic explosion depended upon it.

The American scientists, in contrast, had chosen a different approach to achieve a critical mass. As I explain in my book, “Strange Glow: The Story of Radiation,” the U.S. atomic bomb effort used enriched uranium—uranium that has an increased concentration of the easily split uranium-235—while the Germans used unenriched uranium.
And the Americans chose to slow the neutrons emitted from their
enriched uranium with more readily available graphite, rather than heavy
water. Each approach had its technological trade-offs, but the U.S.
approach did not rely on having to synthesize the extremely scarce heavy
water. Its rarity made heavy water the Achilles’ heel of the German
nuclear bomb program.

Stealthy approach by the Norwegians
Rather than repeating the British strategy of sending dozens of men
in gliders, flying with heavy weapons and equipment (including
bicycles!) to traverse the snow-covered roads, and making a direct
assault at the plant’s front gates, the Norwegians would rely on an alternate strategy.
They’d parachute a small group of expert skiers into the wilderness
that surrounded the plant. The lightly armed skiers would then quickly
ski their way to the plant, and use stealth rather than force to gain
entry to the heavy water production room in order to destroy it with
explosives...MUCH MORE